The following table gives the refractive indices of a few media,

	1	2	3	4	5
Medium:	Water	Crown glass	Rock salt	Ruby	Diamond
Refractive index:	1.33	1.52	1.54	1.71	2.42

Use this table to give an example of:

1. A medium pair so that light speeds up when it goes from one of these medium to another.
2. A medium pair so that light slows down when it goes from one of these medium to another.

Write the formula for a lens connecting image distance (υ), object distance (u) and the focal length (f). How does the lens formula differ from the mirror formula?

Which kind of mirrors are used in the headlights of a motorcar and why?

Show by drawing a ray-diagram that the image of an object formed by a concave lens is virtual, erect and diminished.

Draw a ray diagram to show the path of the reflected ray corresponding to an incident ray which is directed towards the principal focus of a convex. mirror. Mark on it the angle of incidence and the angle of reflection.

The optician’s prescription for a spectacle lens is marked +0.5D. What is the:

1. Nature of spectacle lens?
2. Focal length of spectacle lens?

The boy walks towards the mirror at a speed of 1m/ s. At what speed does his image approach him?

Describe the nature of image formed when the object is placed at a distance of 20cm from a concave mirror of focal length 10cm.

It is desired to obtain an erect image of an object, using concave mirror of focal length of 12cm.
Will the image be smaller or larger than the object? Draw ray diagram to show the formation of image in this case.

Explain why, a real image can be projected on a screen but a virtual image cannot.